1. Technical Field
The present invention relates to spindle motors employing dynamic-pressure bearings in which oil is the working fluid, and to disk drives equipped with such spindle motors. The invention relates in particular to miniature, low-profile spindle motors that drive recording disks 2.5 inches and under, and to disk-drives equipped with such spindle motors.
2. Description of the Related Art
Dynamic-pressure bearings in which the fluid pressure of a lubricating fluid such as oil interposed in between the shaft and the sleeve is exploited in order to support the two letting the one rotate against the other have been proposed to date as bearings for spindle motors employed in disk drives that drive hard disks and like recording disks.
FIG. 1 depicts one example of a spindle motor employing dynamic-pressure bearings. This spindle motor in which conventional dynamic pressure bearings are employed is configured with a pair of axially separated radial bearing sections d, d in between the circumferential surface of the motor shaft b, which is integral with the rotor a, and the inner peripheral surface of the motor sleeve c, into which the shaft b is rotatively inserted. Likewise, a pair of thrust bearing sections g, g is configured in between the upper surface of a disk-shaped thrust plate e that projects radially outward from the circumferential surface of the shaft b on one of its ends, and the flat surface of a step formed in the sleeve c, as well as in between the lower surface of the thrust plate e and a thrust bush f that closes off one of the openings in the sleeve c.
A series of micro-gaps is formed in between the shaft b and thrust plate e, and the sleeve c and thrust bush f, and oil as a lubricating fluid is retained continuously without interruption within these micro-gaps. The oil retained in the micro-gaps is exposed to the air only within a taper-seal area h provided at the upper-end opening (the other opening in the sleeve c) of the gap formed in between the circumferential surface of the shaft b and the inner peripheral surface of the sleeve c. (This sort of oil-retaining structure will be denoted a xe2x80x9cfull-fill structurexe2x80x9d hereinafter.)
The dynamic-pressure bearings further include herringbone grooves d1, d1 and g1, g1 that are linked pairs of spiral striations formed in the radial bearing sections d, d and thrust bearing sections g, g. In response to the rotor a rotating the grooves d1, d1 and g1, g1 generate maximum dynamic pressure in the bearing-section central areas where the spiral striation links are located, thereby supporting loads that act on the rotor a.
A way of charging oil into bearing devices with this sort of full-fill structure, in which difference in air pressure is exploited to replace the air in the micro-gaps with oil by dripping oil in the proper amount into an opening in the bearing in a reduced-pressure environment and thereafter restoring the pressure to normal, is the generally utilized method.
In an oil-charging method of this sort in which difference in air pressure is exploited, air bubbles are kept from remaining behind within the bearing micro-gaps by controlling how much the pressure is reduced and how long the bearing device and the oil are left under the reduced pressure environment. Nevertheless, due to the influence of processing work and assembly tolerances on the bearing-constituting materials, completely discharging air bubbles from the interior of the micro-gaps is problematic, and in some cases air bubbles end up staying mixed into the oil even though assembly of the bearing device has been completed.
Likewise, by vibration being applied to the rotor a during shipping and handling it can happen that air bubbles appear within the oil due to cavitation. Air bubbles produced by such cavitation tend to be especially likely to appear in the environs of the thrust bearing sections g, g.
If the motor is run with air bubbles mixed as they are into the oil, a problem arises that has an impact on the durability and reliability of the spindle motor, in that by and by the air bubbles swell in volume due to elevation in temperature, causing the oil to leak out to the bearing exterior. Another problem that arises has an impact on the rotational precision of the spindle motor, in that owing to the dynamic-pressure-generating grooves provided in the bearing sections coming into contact with the air bubbles, vibration occurs and NRRO (non-repeatable runout) worsens.
At times, moreover, individual air bubbles while rotating together with the rotor a cohere and form circumferentially oriented air pockets. If such an air pocket appears in the thrust bearing sections g, g, the herringbone grooves g1, g1 provided in the thrust bearing sections g, g become exposed to the air, which keeps the predetermined dynamic pressure from being generable and becomes a causative factor giving rise to abnormality in the amount of lift on the rotor a.
An object of the present invention is to render a spindle motor capable of discharging air bubbles from the bearing sections, and at the same time in which miniaturization and slimming in profile are feasible.
Another object of the invention is to render a spindle motor capable of sustaining at or above atmospheric pressure the internal pressure of the oil retained within the bearing clearances, and preventing air bubbles from being generated within the oil.
Still another object is to render a spindle motor that enables the internal pressure of the oil retained within the bearing clearances to balance.
The present invention is also the rendering of a low-profile, low-cost disk drive providing for stabilized spinning of recording disks.
Yet another object of the invention is to render a disk drive of superior reliability and endurance, capable of preventing incidents of read/write errors.
In one example of a spindle motor according to the invention, the rotor has a circular flat face extending radially outward from the circumferential surface of the shaft, and a series of bearing clearances filled with oil is formed in between the flat face of the rotor, and the shaft and a hollow cylindrical bearing member having a bearing hole into which the shaft is rotatively inserted. A thrust bearing section furnished with dynamic pressure grooves is formed in between the end face at an opening in the bearing member, and the flat face of the rotor; and a radial bearing section furnished with dynamic pressure grooves is formed in between the inner peripheral surface of the bearing hole and the circumferential surface of the shaft. In addition, at least one ray-like groove that reaches from the radially inward edge of the dynamic-pressure-generating grooves in the thrust bearing section to the bearing hole is furnished in the bearing member.
This configuration makes it possible to discharge air bubbles that either remain behind or are generated within the oil in a spindle motor utilizing dynamic-pressure bearings having a full-fill structure.
The situation within the oil retained in the gap formed in between the sleeve located radially inward of the thrust bearing section and the flat face of the rotor is that air bubbles stemming from cavitation on account of irregularities in the process of pouring in the oil and vibrations applied during shipping of the motor are liable to appear. Nevertheless, by at least unilaterally forming in the bearing member a ray-like groove that reaches from the radially inward edge of the dynamic-pressure-generating grooves provided in the thrust bearing section, to the bearing hole, when the motor rotates the air bubbles are stirred and minced by the ray-like groove, making it so that they are readily discharged.
In particular, the ray-like groove causes a circumferentially oriented pressure gradient to appear intermittently in the dynamic pressure generated in the thrust bearing section; and the rotation of this pressure gradient develops a random pressure distribution in the region radially inward beyond the thrust bearing section, while maintaining positive pressure. By the air bubbles being swept into a rotating random pressure distribution like this, the air bubbles are broken up until they are sufficiently smaller than the clearance dimension of the gap formed in between the flat face of the rotor and the end face of the bearing member, and are discharged toward the radially outer side of the thrust bearing section, where the oil internal pressure relatively low.
In one example of a disk drive according to the present invention is a recording-disk-spinning spindle motor in which the rotor has a circular flat face extending radially outward from the circumferential surface of the shaft, and a series of bearing clearances filled with oil is formed in between the flat face of the rotor, and the shaft and a hollow cylindrical bearing member having a bearing hole into which the shaft is rotatively inserted. A thrust bearing section furnished with dynamic pressure grooves is formed in between the end face at an opening in the bearing member, and the flat face of the rotor; and a radial bearing section furnished with dynamic pressure grooves is formed in between the inner peripheral surface of the bearing hole and the circumferential surface of the shaft. In addition, at least one ray-like groove that reaches from the radially inward edge of the dynamic-pressure-generating grooves in the thrust bearing section to the bearing hole is furnished in the bearing member.
From the following detailed description in conjunction with the accompanying drawings, the foregoing and other objects, features, aspects and advantages of the present invention will become readily apparent to those skilled in the art.